The present invention relates to a novel lens material. More specifically, it relates to a halogen-containing lens having a high refractive index and a low dispersion.
Various inorganic glass lenses have been conventionally used in optical instruments and devices. Plastic lenses however are beginning to be widely used together with inorganic glass lenses because of their light weight, workability, stability, dyeability, mass productivity, possibility of low cost, etc.
Of the physical properties required of lenses, a high refractive index and a low dispersion are extremely important. For example, the high refractive index of the lenses is effective not only for making compact and light weight a lens system constituting an important component in an optical instrument or device such as a microscope, a camera, a telescope, or spectacle lenses but also for keeping aberration of spherical surfaces and the like small. On the other hand, needless to say, low dispersion (high Abbe's number) of lenses is extremely important for reducing chromatic aberration.
However, in the case of plastic lenses, also, there is a tendency for high refractive index lenses to exhibit high dispersion and low refractive index lenses to exhibit low dispersion. For example, a diethyleneglycol bisallylcarbonate resin (hereinafter referred to as CR-39), which is most widely used at present as a material for spectacle plastic lenses, exhibits a very low refractive index of n.sub.D.sup.20 =1.50. Polymethyl methacrylate which is partially used as a lens material exhibits a high Abbe's number of .nu.=60 but a low refractive index of n.sub.D.sup.20 =1.49 as does the CR-39. Polystyrene (n.sub.D.sup.20 =1.59, .nu.=30.4) and polycarbonate (n.sub.D.sup.20 =1.59, .nu.=29.5), which are said to have a relatively high refractive index and low dispersion, are unsatisfactory with regard to the other physical properties required of lens materials. For example, polystyrene has a poor surface hardness and solvent resistance, and the polycarbonate has a poor surface hardness and impact resistance. Further, polynaphthyl methacrylate (n.sub.D.sup.20 =1.64) and polyvinyl naphthalene (n.sub.D.sup.20 =1.68), which exhibit a high refractive index, have low Abbe's numbers of .nu.=24 and .nu.=20, respectively. All of these lens materials are accompanied by various problems.
Recently, halogen-substituted bisphenol A derivatives have been used as plastic lens material having high refractive indexes. For example, such lens materials are known from Japanese Unexamined Patent Publication Nos. 58-28117 and 57-54901. Although these halogen-substituted bisphenol A derivatives are characterized by high refractive indexes, no reference is made to this Abbe's numbers.
Accordingly, there has been a need for plastic lens materials of excellent high refractive index, low dispersion, transparency, and other important properties.